Draw transparent activity over android application

Issue

I'm trying to create an android Activity that hooks into the system's ActionProcessText intent. The goal is to display my Activity's layout above the currently running application. The Activity is starting just fine, but it doesn't show up on top of the running application.

Google Translate does this already and I confirmed it does not have the Display over other apps permission.

Screen recording showing the above in action - https://i.imgur.com/Q9lVI61.mp4

Here is my activity (written using Xamarin):

[Activity(Label = "@string/app_name", Exported = true)]
[IntentFilter(new[] { Intent.ActionProcessText, Intent.CategoryDefault }, DataMimeType = "text/plain")]
public class LookupActivity : Activity
{
    public override void OnCreate(Bundle? savedInstanceState, PersistableBundle? persistentState)
    {
        base.OnCreate(savedInstanceState, persistentState);
        var data = this.Intent.GetCharSequenceExtra(Android.Content.Intent.ExtraProcessText);
    }
}

and also my layout:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".LookupActivity"
    android:alpha="0.2">
 
    <TextView
        android:id="@+id/msg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
 
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginTop="16dp"
        android:text="Button"
        android:onClick="OnButtonClicked"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/msg"
        app:layout_constraintVertical_bias="0.025" />
 
</android.support.constraint.ConstraintLayout>

My thinking was that if I set the Alpha to something low like 0.2 it would imitate the Google Translate shadow background.

Here is what it looks like when I select my application from the same context menu:

Solution

You can add a style to file styles.xml as follows:

<style name="AppTheme1" parent="Theme.MaterialComponents.Light.DarkActionBar">

            <item name="android:windowIsTranslucent">true</item>

            <item name="android:windowBackground">@android:color/transparent</item>

            <item name="android:windowContentOverlay">@null</item>

            <item name="android:windowNoTitle">true</item>

            <item name="android:windowIsFloating">true</item>

            <item name="android:backgroundDimEnabled">false</item>

            <!-- Customize your theme here. -->

            <item name="android:windowIsFloating">true</item>

      </style>

And apply it to your activity:

 [Activity(Label = "@string/app_name", Exported = true,Theme = "@style/AppTheme1" )]

Answered By - Jessie Zhang -MSFT